1. Field of the Invention
The present invention relates to a connection structure and a connection method for connecting a differential signal transmission cable to a circuit board.
2. Description of the Related Art
In servers, routers, and other storage devices for high speed digital signal transmission at several Gbit/s or more, a differential signal transmission has been used for a signal transmission between equipments or between substrates (circuit boards) in an equipment.
The differential signal transmission (differential signaling) is to transmit two 180° phase-inverted signals through respective ones of a pair of signal line conductors, and to synthesize and output a difference between the two 180° phase-inverted signals received at a receiver side. Since electric currents transmitted through the pair of signal line conductors are flown along directions opposite to each other, it is possible to reduce an electromagnetic wave emitted from transmission paths. Further, in the differential signal transmission, external noises are superimposed on the two signal line conductors equally, so that it is possible to cancel (remove) the effect of the external noises by synthesizing and outputting the difference between the two 180° phase-inverted signals at the receiver side. For the aforementioned reasons, the differential signal transmission has been often used for a high speed digital signal transmission.
FIG. 20 shows an example of a conventional differential signal transmission cable 201, which is often used for the differential signal transmission, comprising a pair of signal line conductors 202, an insulator 203 covering the pair of signal line conductors 202, an outer conductor 204 provided around a circumference of the insulator 203, and a sheath 205 provided around a circumference of the outer conductor 204.
The outer conductor 204 may be formed by winding a conductive film-attached tape (shield tape) around the insulator 203, by covering the insulator 203 with braided wires, or the like. The sheath 205 may be formed by winding an insulating tape around the outer conductor 204, by extrusion-coating a resin around the outer conductor 204, or the like.
In the differential signal transmission cable 201, the pair of signal line conductors 202 are juxtaposed (arranged in parallel with each other). According to this structure, a difference in physical length between the pair of signal line conductors is small so that signal attenuation at high frequencies is small compared with those in a differential signal transmission cable comprising a twisted pair of signal line conductors. Further, since the outer conductor 204 is provided to cover the pair of signal line conductors 202, even if a metallic member is placed near the cable, the characteristic impedance will not be unstable. In addition, the noise resistance property (noise immunity) is also high. From these advantages, the differential signal transmission cable 201 has been often used for a relatively high-speed and short-distance signal transmission.
When the differential signal transmission cable 201 is connected to a circuit board in equipment, as shown in FIGS. 21 and 22, the sheath 205, the outer conductor 204, and the insulator 203 are sequentially peeled off from the differential signal transmission cable 201 by multi-stage stripping. Each of the pair of signal line conductors 202 is solder-connected (i.e. connected by soldering) to each of signal pads 212 formed on a circuit board 211, and the outer conductor 204 is directly solder-connected to a ground pad 213 formed on the circuit board 211.
Japanese Patent Laid-Open No. 2004-71384 (JP-A 2004-71384) discloses a similar connection method and a connection structure for connecting a difference signal transmission cable to a circuit board.